Pulse Generator Circuit

ABSTRACT

A pulse generator circuit is disclosed that is optimized for printed, solution-processed thin film transistor processing. In certain embodiments, the circuit comprises dual thin film transistors that operate as a diode and resistor, respectively. Optionally, a third thin film transistor may be provided to operate as a pass transistor in response to an enable signal. The elements of the circuit are configured such that a rising pulse on an input node triggers an output pulse on an output node in the manner of a monostable multivibrator.

BACKGROUND

The present disclosure is related to digital electronic circuits, andmore specifically to a pulse generator circuit optimized for printed,solution processed thin-film devices.

A pulse generator, also called a monostable multivibrator or one-shot,is a common element of many circuits in a wide range of applications.One common use is for switch debouncing. Another is as a reset signalgenerator. The input to a one-shot is an edge or pulse and the output isa positive or negative voltage pulse. The duration and magnitude of thepulse can be fixed or settable and are generally constrained to fallwithin ranges specified for the application. FIG. 1 shows a timingdiagram of an example of a one-shot circuit.

A common circuit implementation of a monostable multivibrator includesan inverter and a NAND or NOR gate. FIG. 2 is an example of such animplementation. This circuit is a rising-edge-triggered negative pulsegenerator. In this circuit, input signal In is normally low, andinverter output D is high, making output signal Out high. When a risingedge is sent to In, output Out switches to low until the edge propagatesthrough the inverter to D. Once D switches to low, Out returns to thehigh state. The duration of the pulse is determined by the propagationdelay through the inverter. This can be controlled by the sizes of thetransistors making up the inverter and NAND gate and/or by includingadditional delay elements, such as additional inverters or capacitors,to the D signal. Of course, many other implementations are known in theart.

There is a desire to produce devices such as the aforementionedmonostable multivibrator using printed thin-film processes such as, butnot limited to, those employing organic thin film (OTF) materialsystems. OTF fabrication processes are much less mature than crystallinesilicon technologies, and direct implementation of conventionalcomplementary designs is challenging due to the relatively low yield,high variability, and instability of devices formed by printed OTFprocesses. For example, in certain of such process reliable fabricationof all integrated devices in a single process is problematic. Further,according to some OTF processes, only one or the other of N- andP-channel devices may be formed (not both simultaneously). In processescapable of producing both N- and P-channel devices, one device typeoften has significantly higher performance than the other. And,process-based limits on device size in combination with large parasiticcapacitances limit design of devices having desired pulse widths.

In light of these limitations, there is a need in the art for a devicedesign capable of use within the context of OTF processes, such ascircuit designs that include a minimum number of thin-film transistors(TFTs) and a single polarity. Such are disclosed herein.

SUMMARY

Accordingly, the present disclosure is directed to circuit designs forconverting an edge output by a sensor to a signal that addresses thedifficulties of forming such circuits using solution-based and printedprocesses. The circuits provide a pulse sustained above a voltagethreshold for a minimum time interval. Applications include clockingflip-flops, generating reset signals, polarizing a memory cell, and soon. The devices may be fabricated in an all-additive inkjet process. Forthe clarity and simplicity, processing using organic material (organicthin-film, OTF) is referred to below as an example of solution-basedprinted process, although it will be appreciated that many differenttypes of solutions and materials, whether organic or inorganic, arecontemplated herein and within the scope of the present disclosure.Therefore, OTF and organic material will be understood to be examplesonly, and the scope of the disclosure not limited thereby.

According to one aspect of the disclosure, an electronic pulse-generatorcircuit comprises: an input node; a capacitor communicatively connectedat to the input node and to a pulse line; a first thin film transistorhaving a channel formed of a first polarity organic semiconductormaterial, a first side of the channel communicatively connected to afirst voltage source, a second side of the channel communicativelyconnected to the pulse line, the first thin film transistor configuredto function as a diode; a second thin film transistor having a channelformed of the first polarity organic semiconductor material, a firstside of the channel communicatively connected to the pulse line, asecond side of the channel communicatively connected to a second voltagesource (e.g., ground), the second thin film transistor configured tofunction as a resistor; and an output node communicatively connected toreceive a pulse from the pulse line.

Implementations of this aspect may also include a third thin filmtransistor having a channel formed of the first polarity organicsemiconductor material, a first side of said channel communicativelyconnected to the pulse line, a second side of the channelcommunicatively connected to the output node, and further comprising agate communicatively connected to a first enable signal line.

According to another aspect of the disclosure, the first polarityorganic semiconductor material is p-type.

Implementations may also include the first thin film transistor furthercomprising a gate communicatively connected to the pulse line at thecapacitor, and further wherein the second thin film transistor furthercomprises a gate communicatively connected to the second voltage source(e.g., ground).

Other implementations of the present disclosure are also provided anddiscussed in greater detail, below. Thus, the above is merely a briefsummary of a number of unique aspects, features, and advantages of thepresent disclosure. The above summary is not intended to be nor shouldit be read as an exclusive identification of aspects, features, oradvantages of the claimed subject matter. Therefore, the above summaryshould not be read as imparting limitations to the claims nor in anyother way determining the scope of said claims.

It should be noted that the present disclosure focuses onsolution-proceed devices. These are devices having one or more layersformed from the deposition of materials solution phase, which solidify(such as by evaporation). One form of solution processing is printing ofpatterned solution. Materials capable of solution processing may beeither organic or inorganic. While this disclosure uses printed organicsemiconductor technologies as an example, the invention is equallyapplicable to other process technologies. Furthermore, the invention canbe implemented in other TFT technologies that are not solution based.Therefore, in this disclosure, references to solution processing,printing, and organic materials should be read as examples, not limitingdistinctions.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings appended hereto like reference numerals denote likeelements between the various drawings. While illustrative, the drawingsare not drawn to scale. In the drawings:

FIG. 1 is a timing diagram of a positive-edge-triggered one-shot circuitwith pulse duration, d, and voltage amplitude, v, as known in the art.

FIG. 2 is an implementation of a monostable multivibrator including aninverter and a NAND or NOR gate as known in the art.

FIG. 3A is a schematic illustration of one embodiment of a pulsegenerator circuit, tailored for fabrication by organic thin-filmprocesses, according to the present disclosure.

FIG. 3B is a schematic illustration of an equivalent circuit to thatshown in FIG. 3A of an embodiment of a pulse generator circuit, tailoredfor fabrication by organic thin-film processes, according to the presentdisclosure.

FIG. 4 is a schematic illustration of an alternate embodiment of a pulsegenerator circuit, tailored for fabrication by organic thin-filmprocesses, according to the present disclosure.

FIG. 5 is a plot of a simulation illustrating various voltages on linesas a function of time for the embodiment shown in FIG. 4.

FIG. 6 is a plot of In and Out voltages for an actual example of thecircuit of FIG. 4 plotted against time.

FIG. 7 is a schematic illustration of another alternate embodiment of apulse generator circuit, tailored for fabrication by organic thin-filmprocesses, according to the present disclosure.

FIG. 8 is a schematic illustration of yet another alternate embodimentof a pulse generator circuit, tailored for fabrication by organicthin-film processes, according to the present disclosure.

FIG. 9 is a schematic illustration of still another alternate embodimentof a pulse generator circuit, tailored for fabrication by organicthin-film processes, according to the present disclosure.

FIG. 10 is a schematic illustration of a still further alternateembodiment of a pulse generator circuit, tailored for fabrication byorganic thin-film processes, according to the present disclosure.

FIG. 11 is a schematic illustration of an additional alternateembodiment of a pulse generator circuit, tailored for fabrication byorganic thin-film processes, according to the present disclosure.

DETAILED DESCRIPTION

We initially point out that description of well-known startingmaterials, processing techniques, components, equipment and otherwell-known details may merely be summarized or are omitted so as not tounnecessarily obscure the details of the present disclosure. Thus, wheredetails are otherwise well-known, we leave it to the application of thepresent disclosure to suggest or dictate choices relating to thosedetails.

With reference to FIG. 3A, there is shown therein a first embodiment ofa pulse generator circuit 10 tailored for fabrication by organicthin-film (OTF) processes. Circuit 10 comprises an input In, and outputOut, a capacitor 12, a first thin-film transistor (TFT) 14, and a secondTFT 16, each of the same polarity. Circuit 10 of FIG. 3A is intended tomodel a circuit 18 shown in FIG. 3B, in that TFT 14 models resistor 20and TFT 16 models diode 22, with operation as follows. A rising edge onIn of circuit 10 is passed though a high-pass filter made up ofcapacitor 12 and TFT 14 (e.g., resistor 20) to Out. Diode bias V_(b) isset to a voltage such that TFT 16 (e.g., diode 22, FIG. 3B) prevents Outfrom being negative. Voltage V_(b) is approximately one diode-drop aboveground. Depending on the implementation, negative voltages may beallowed on signal Out, in which case V_(b) can simply be set to ground.Other values of V_(b) may also be acceptable, depending on theapplication. In some implementations, one or both of the TFTs 14, 16 canbe replaced by their equivalent components, 20 and 22, respectively,where diodes and resistors are available. Also capacitor 12 can beimplemented in the OTF process (for example, with gate dielectricbetween gate and source/drain metal layer with no semiconductor) orseparately.

FIG. 4 shows a first alternate embodiment of a pulse generator circuit24 tailored for fabrication by organic thin-film (OTF) processes.Circuit 24 comprises an input In, and output Out, a capacitor 26, afirst thin-film transistor (TFT) 28 (acting as a resistor), and a secondTFT 30, each of the same polarity, similar to the embodiment illustratedand described above with regard to FIG. 3A. Circuit 24 further comprisesa pass TFT 32 connecting the output of the circuit to a load. A risingedge on In generates a pulse at P. The generation of a complimentarynegative pulse with a falling edge is prevented by TFT 30, which issized much wider than TFT 28 to function as a diode. The dc value of Pis given by V_(b) minus the threshold voltage of TFT 30 (V₃₀), and maybe set to ground (but can be other values). In particular, if anadditional voltage rail is not available or desired, V_(b) can be tiedto ground and P clamped at −V₃₀. A low signal on EnBar will pass thepulse P to Out through TFT 32. (The on-characteristic of TFT 32 willfurther filter the pulse signal.)

In principal, the sizes of TFTs such as 14 and 16, 28 and 30, etc. aredetermined based on the source impedance seen at In. The transferfunction from the source to P is given by

$f = \frac{{sCR}_{x}}{{{sC}\left( {R_{x} + R_{s}} \right)} + 1}$

where R_(x) is the channel resistance of TFT 28 for a positive pulse andof TFT 30 for a negative pulse, R_(s) is the source impedance, C is thecapacitance of capacitor 26, and s is the Laplace parameter. The sourceimpedance Rs is the output impedance of the circuit driving the pulsegenerator and is not part of the pulse generator circuit itself. At highfrequency (s→∞), the transfer function is approximately 1 whenR_(x)>>R_(s) and approximately 0 when R_(x<<R) _(s). TFT 30 acts as adiode in the sense that it is off during a positive pulse and on duringa negative pulse. Thus, if R_(on) of TFT 28 is much greater than R_(s),and R_(on) of TFT 30 is much less than R_(s), positive pulses will begenerated while negative pulses are shunted. In practice, theon-resistance of TFT 32 is usually non-negligible and will be accountedfor in the transfer function analysis.

The circuit described above may be fabricated on a flexible polyethylenenaphthalate substrate by an additive OFT process that includes ink-jetdeposition of the metal and semiconductor layers. The capacitor may be aparallel plate structure formed by the gate dielectric and thesource-drain and gate metals. Other substrate materials and structuresmay be employed depending on the design criteria and application ofembodiments of the present disclosure.

Alternatively, if both n- and p-channel devices are available, atransmission gate can be used. By placing multiple pass transistors inparallel, the pulse can be selectively connected to one or more ofseveral outputs.

The sizes of TFTs 14, 16 of embodiment 10 (FIG. 3A) and TFTs 28, 30, 32of embodiment 24 (FIG. 4) are highly dependent on the application andimplementation of the respective circuits, in particular on thecharacteristics of the TFTs themselves (threshold voltage, mobility,etc.), the process design rules (minimum channel length, availablechannel widths), and the load resistance and capacitance. Additionally,they are dependent on the desired pulse duration and shape.

FIG. 5 shows In, EnBar, P, and Out values plotted against time in asimulation of circuit 24 (FIG. 4) for a printed OTF process. In thissimulation, a 20-volt input step, V_(b)=0 volts, and a 10 pF capacitiveload were used. A capacitance of capacitor 26 was 200 pF. Each of TFTs28, 30, and 32 had a channel length of 35 μm. The channel widths of TFTs28, 30 and 32 were 200 μm, 6 mm, and 400 μm, respectively. In general,the length and width are process dependent. According to one embodiment,length may range from 2 μm to 200 μm, and widths may range from 100 μmto 1 cm. It will be noted that a rising pulse on In (at approximately 58ms) triggers a pulse on Out when EnBar is low.

FIG. 6 shows measured output of circuit 24 (FIG. 4). Each of TFTs 28,30, and 32 had a approximate channel length of 35 μm. The channel widthsof TFTs 28, 30 and 32 were approximately 200 μm, 6 mm, and 400 μm,respectively. The voltage V_(b) was 3.5 volts. Capacitor 26 had a valueof 200 μF. Again, it will be noted that a rising pulse on In (at 40 ms)triggers an output pulse.

Illustrated in FIGS. 7 through 11 are various alternate embodiments of apulse generator circuit tailored for fabrication by OTF processes. Morespecifically, FIG. 7 includes TFTs 42, 44, and 46 similar to thosedescribed with reference to FIG. 4. In addition, the circuit of FIG. 7includes an additional enable TFT 48, enabled when a voltage En is high.In typical operation, signal En is the complement of EnBar at all times.When En is low (disabled), TFT 48 serves to aid in clamping Out nearground. FIG. 8 is an alternate embodiment for filtering the pulse on Outin which TFT 42 from FIG. 7 has been eliminated, leaving TFTs 52, 54,and 56. In function, TFT 56 serves in place of TFT 28 of FIG. 4. Here,Ena at the gate of TFT 56 is an analog voltage that sets the effectiveresistance of TFT 56. FIG. 9 is a modification of the circuit of FIG. 4including TFTs 62, 64, 66, in which TFT 62 corresponding to the resistor(20 of FIG. 3B) has been relocated to the output side of TFT 66.

FIG. 10 is an illustration of a N-channel TFT implementation of thecircuit illustrated in FIG. 3A, including N-channel TFTs 72, 74. FIG. 11is an illustration of a N-channel TFT implementation of the circuitillustrated in FIG. 4, including N-channel TFTs 82, 84, 86.

The physics of modern electrical devices and the methods of theirproduction are not absolutes, but rather statistical efforts to producea desired device and/or result. Even with the utmost of attention beingpaid to repeatability of processes, the cleanliness of manufacturingfacilities, the purity of starting and processing materials, and soforth, variations and imperfections result. Accordingly, no limitationin the description of the present disclosure or its claims can or shouldbe read as absolute. The limitations of the claims are intended todefine the boundaries of the present disclosure, up to and includingthose limitations. To further highlight this, the term “substantially”may occasionally be used herein in association with a claim limitation(although consideration for variations and imperfections is notrestricted to only those limitations used with that term). While asdifficult to precisely define as the limitations of the presentdisclosure themselves, we intend that this term be interpreted as “to alarge extent”, “as nearly as practicable”, “within technicallimitations”, and the like.

While examples and variations have been presented in the foregoingdescription, it should be understood that a vast number of variationsexist, and these examples are merely representative, and are notintended to limit the scope, applicability or configuration of thedisclosure in any way. Various of the above-disclosed and other featuresand functions, or alternative thereof, may be desirably combined intomany other different systems or applications. Various presentlyunforeseen or unanticipated alternatives, modifications variations, orimprovements therein or thereon may be subsequently made by thoseskilled in the art which are also intended to be encompassed by theclaims, below.

Therefore, the foregoing description provides those of ordinary skill inthe art with a convenient guide for implementation of the disclosure,and contemplates that various changes in the functions and arrangementsof the described examples may be made without departing from the spiritand scope of the disclosure defined by the claims thereto.

What is claimed is:
 1. An electronic pulse-generator circuit,comprising: an input node; a capacitor communicatively connected to saidinput node and to a pulse line; a first thin film transistor having achannel formed of a first polarity solution-processed semiconductormaterial, a first side of said channel communicatively connected to afirst voltage source, a second side of said channel communicativelyconnected to said pulse line, said first thin film transistor configuredto function as a diode; a second thin film transistor having a channelformed of said first polarity solution-processed semiconductor material,a first side of said channel communicatively connected to said pulseline, a second side of said channel communicatively connected to asecond voltage source, said second thin film transistor configured tofunction as a resistor; and an output node communicatively connected toreceive a pulse from said pulse line.
 2. The electronic pulse-generatorcircuit of claim 1 wherein said first polarity solution-processedsemiconductor material is P-type.
 3. The electronic pulse-generatorcircuit of claim 1, further comprising a third thin film transistorhaving a channel formed of said first polarity solution-processedsemiconductor material, a first side of said channel communicativelyconnected to said pulse line, a second side of said channelcommunicatively connected to said output node, and further comprising agate communicatively connected to a first enable signal line.
 4. Theelectronic pulse-generator circuit of claim 3, further comprising afourth thin film transistor having a channel formed of said firstpolarity solution-processed semiconductor material, a first side of saidchannel communicatively connected to said pulse line at said outputnode, a second side of said channel communicatively connected to a thirdvoltage source, and further comprising a gate communicatively connectedto a second enable signal line.
 5. The electronic pulse-generatorcircuit of claim 3, wherein said first side of said channel of saidsecond thin film transistor is communicatively connected to said pulseline at said output node.
 6. The electronic pulse-generator circuit ofclaim 5, wherein said second thin film transistor further comprises agate communicatively connected to a third enable signal line.
 7. Theelectronic pulse-generator circuit of claim 3, wherein said secondvoltage source is ground.
 8. The electronic pulse-generator circuit ofclaim 1, wherein said first polarity solution-processed semiconductormaterial is N-type.
 9. The electronic pulse-generator circuit of claim8, wherein said first thin film transistor comprises a gatecommunicatively connected to said first voltage source, and furtherwherein said second thin film transistor further comprises a gatecommunicatively connected to said pulse line, said capacitor, and saidsecond side of said channel of said first thin film transistor.
 10. Theelectronic pulse-generator circuit of claim 1, wherein said first thinfilm transistor further comprises a gate communicatively connected tosaid pulse line, said capacitor, and said second side of said channel ofsaid first thin film transistor, and further wherein said second thinfilm transistor further comprises a gate communicatively connected toground.
 11. The electronic pulse-generator circuit of claim 1, whereinsaid first polarity solution-processed semiconductor material is N-type.12. The electronic pulse-generator circuit of claim 11, wherein saidfirst thin film transistor comprises a gate communicatively connected tosaid voltage source, and further wherein said second thin filmtransistor further comprises a gate communicatively connected to saidpulse line, said capacitor, and said second side of said channel of saidfirst thin film transistor.
 13. An electronic pulse-generator circuit,comprising: an input node; an output node; a capacitor communicativelyconnected to said input node and to a pulse line; a first thin filmtransistor having a channel formed of a p-type solution-processedsemiconductor material, a first side of said channel communicativelyconnected to a voltage source, a second side of said channelcommunicatively connected to said pulse line, said first thin filmtransistor configured to function as a diode; a second thin filmtransistor having a channel formed of p-type solution-processedsemiconductor material, a first side of said channel communicativelyconnected to said pulse line, a second side of said channelcommunicatively connected to ground, said second thin film transistorconfigured to function as a resistor; and a third thin film transistorhaving a channel formed of p-type solution-processed semiconductormaterial, a first side of said channel communicatively connected to saidpulse line, a second side of said channel communicatively connected tosaid output node, and further comprising a gate communicativelyconnected to a first enable signal line.
 14. The electronicpulse-generator circuit of claim 13, further comprising a fourth thinfilm transistor having a channel formed of p-type solution-processedsemiconductor material, a first side of said channel communicativelyconnected to said pulse line at said output node, a second side of saidchannel communicatively connected to ground, and further comprising agate communicatively connected to a second enable signal line.
 15. Theelectronic pulse-generator circuit of claim 13, wherein said first sideof said channel of said second thin film transistor is communicativelyconnected to said pulse line at said output node.
 16. The electronicpulse-generator circuit of claim 15, wherein said second thin filmtransistor further comprises a gate communicatively connected to a thirdenable signal line.
 17. The electronic pulse-generator circuit of claim16, wherein said third enable signal line is communicatively connectedto ground.
 18. An electronic pulse-generator circuit, comprising: aninput node; an output node; a capacitor communicatively connected tosaid input node and to a pulse line; a first thin film transistor havinga channel formed of a printed p-type organic semiconductor material, afirst side of said channel communicatively connected to a voltagesource, a second side of said channel communicatively connected to saidpulse line, said first thin film transistor configured to function as adiode; a second thin film transistor having a channel formed of aprinted p-type organic semiconductor material, a first side of saidchannel communicatively connected to said pulse line, a second side ofsaid channel communicatively connected to ground, said second thin filmtransistor configured to function as a resistor; a third thin filmtransistor having a channel formed of a printed p-type organicsemiconductor material, a first side of said channel communicativelyconnected to said pulse line, a second side of said channelcommunicatively connected to said output node, and further comprising agate communicatively connected to a first enable signal line; and afourth thin film transistor having a channel formed of a printed p-typesemiconductor material, a first side of said channel communicativelyconnected to said pulse line at said output node, a second side of saidchannel communicatively connected to ground, and further comprising agate communicatively connected to a second enable signal line.
 19. Theelectronic pulse-generator circuit of claim 18, wherein said first sideof said channel of said second thin film transistor is communicativelyconnected to said pulse line at said output node.
 20. The electronicpulse-generator circuit of claim 19, wherein said second thin filmtransistor further comprises a gate communicatively connected to ground.